How do you drift consistently

/snake

by playing more

Being more specific would help.

Do you mean getting the boost? Cus if not gonna have to be specific...

Literally just practice snaking. It's hard when you first start but you improve quickly enough. Try doing some time trials.

I mean 50% of the time I don't dont get the boost because it doesn't charge quick enough

I have some advice that is not talked about a lot but works for me. Try watching good speedruns and time trials of this game with the volume UP. Listen to the rhythm that the sparks make. Now, play the game yourself with the volume UP. Try to make your rhythm as close as possible without rushing; it is better to get a drift boost a little slow then to miss the drift boost completely.
For example, watch this:https://m.youtube.com/watch?v=TOIUYeA3GBc with the volume up. Listen to the "wsh whoo" that the drifting sparks make. The timing of the audio is when you have to press in the direction of your drift. For example, if you are drifting to the right, You hop, press right, then left, then RIGHT ("WSH" SOUND), then left, then RIGHT("WHOO" SOUND).

Another tip that not many talk about is that you want to get rid of your red sparks and boost as soon as possible. This helps you snake and connect your drift boosts. You want to release your drift boost IMMEDIATLY as you get the red sparks, unless you need to purposefully wait to make the right path.

Also, practicing snaking on GCN Luigi circuit is pretty helpful.

Also is it easier with the dpad or joypad on 3ds

I use stick but I think it is preference. Though my guess would be too use whatever you are comfortable with and you can move the fastest.

dpad is wayyyy easier for me but I know the positioning isn't great for long snaking sessions.

D-pad in the end is objectively slightly better. In the event that you need to rapidly press LEFT or RIGHT, d pad lets you mash, while with stick you have to slide to the left then return to neutral. For example, if you need to (non-drift) turn to the left at an angle that is too small for holding left, and too great for slowly pressing left on and off, you can mash left really quickly with d pad. In the end it's only a tiny difference.

Also, in my opinion, I feel that you have better control of exactly when left and right are being pressed, while stick feels more unexact.